1. Field of the Invention
The present invention relates in general to a key switch provided on a keyboard or data input device used for a word processor and a personal computer, for example. More particularly, this invention is concerned with a key switch which is easy to assemble and which has a high degree of operating stability.
2. Discussion of the Prior Art
In a conventional key switch, the keytop is supported vertically movably for a switching action such that a key stem extending from the underside of the keytop is slidably supported and guided by a suitable guide portion formed on a holder plate. The operating stability of the key switch or keytop is improved by increasing the length of a guided portion of the key stem at which the key stem is slidably guided by the guide portion. On the other hand, the thickness of the keyboard is inevitably increased with an increase in the length of the guided portion of the key stem.
Recently, personal computers, word processors and similar electronic devices are required to have reduced size and weight for easy carrying or transportation. Keeping pace with this requirement, there is a growing need for reducing the thickness of the keyboard used as a data input device for such electronic devices.
The need indicated above may be satisfied by reducing the length of the guided portion of the key stem. However, this may lead to easy sticking or sliding instability of the key stem, and deteriorated operating stability of the key switch.
In view of the drawbacks of the conventional key switch and the growing need for reduced thickness of the keyboard, there was proposed a key switch which has a scissors-type support linkage for movably supporting the keytop for a switching action, in place of a conventionally used key stem slidably supported and guided by a holder plate. An example of such key switch is disclosed in U.S. Pat. No. 5,280,147.
The key switch having such scissors-type support linkage will be described by reference to FIGS. 14-16.
As shown in FIG. 14, the key switch includes a Keytop 101 made of a resin material. The Keytop 101 has a pair of spaced-apart front bearing portions 102 formed at a front end portion of its underside, and a pair of spaced-apart rear bearing portions 103 formed at a rear end portion of the underside. Each of the front bearing portions 102 has a circular engaging hole 104, and each of the rear bearing portions 103 has an elongated engaging groove 105. The key switch further includes a pair of spaced-apart rear bearing portions 126 formed on a holder plate 125, and a pair of spaced-apart front bearing portions 127 also formed on the holder plate 125. The holder plate 125 is made of a resin material. The front bearing portions 127 are spaced apart from the rear bearing portions 126 in a direction perpendicular to a direction in which the front bearing portions 127 are spaced apart from each other. The rear bearing portions 126 have respective elongated engaging grooves 128, while the front bearing portions 127 have respective circular engaging holes 129.
The keytop 101 is movably connected to the holder plate 125 through a scissors-type support linkage 106 consisting of a first link 107 and a second link 108 which are pivotally connected to each other as described below. These links 107, 108 are each formed of a resin material. The first link 107 has a pair of stationary pivot pins 113, 114 as its front or upper end, and a pair of sliding pins 115, 116 at its rear or lower end. The stationary pivot pins 113, 114 engage the respective circular engaging holes 104, while the sliding pins 115, 116 are received in the respective engaging grooves 128. The second link 108 has a pair of stationary pivot pins 121, 122 at its front or lower end, and a pair of sliding pins 123, 124 at its rear or upper end. The stationary pivot pins 121, 122 engage the respective engaging holes 129, while the sliding pins 123, 124 are received in the respective engaging grooves 105. Thus, the keytop 101 is connected to the holder plate 125 by the support linkage 106.
The two links 107, 108 are pivotally connected to each other at a pivot 132 as shown in FIG. 14. When the keytop 101 is pressed, the two links 107, 108 are pivoted about the pivot 132, and the pivot 132 is lowered and forced onto a cup-shaped rubber spring 131 formed on the holder plate 125, whereby the rubber spring 131 is collapsed for a switching action as well known in the art. Briefly, a movable electrode attached to the top wall of the rubber spring 131 is forced into contact with stationary electrodes disposed within the rubber spring 131.
As shown in FIG. 15, the first link 107 has a central portion 109, and two end portions 110, 111 at the opposite ends of the central portion 109 such that the portions 109-111 are integral with each other. The central portion 109 has a shaft 112 laterally extending from one of its opposite sides. As described below, the shaft 112 is inserted through a hole 120 formed through the second link 108 when the two links 107, 108 are assembled into the support linkage 106. The end portion 110 has opposite longitudinal ends 110A, 110A from which the two stationary pivot pins 113, 114 extend for engagement with the engaging holes 104. The end portion 111 is generally C-shaped as viewed in the plan view of FIG. 15, and has opposite longitudinal ends 111A, 111A from which the sliding pins 115, 116 extend for sliding engagement with the engaging grooves 128.
As shown in FIG. 16, the second link 108 has a central portion 117, and two end portions 118, 119 at the opposite ends of the central portion 117 such that the portions 117-119 are integral with each other. The central portion 117 has the above-indicated hole 120 through which the shaft 112 of the first link 107 is inserted. The end portion 118 is generally C-shaped as seen in the plan view of FIG. 16, and has opposite longitudinal ends 118A, 118A from which the stationary pivot pins 121, 122 extend for engagement with the engaging holes 129. The end portion 119 has opposite longitudinal ends 119A, 119A from which the sliding pins 123, 124 extend for sliding engagement with the engaging grooves 105.
The support linkage 106 is prepared by assembling the first and second links 107, 108 such that the shaft 112 extending from the central portion 109 of the link 107 is inserted through the hole 120 formed through the central portion 117 of the link 108. The shaft 112 cooperate with the hole 120 to constitute the pivot 132 indicated in FIG. 14, about which the two links 107, 108 are pivotable relative to each other.
The key switch constructed as described above suffers from difficulty in the assembling process. That is, it is difficult and cumbersome to connect the support linkage 106 to the holder plate 125, and connect the keytop 101 to the support linkage 106.
In assembling the key switch of FIG. 14, the support linkage 106 is first produced by assembling the first and second links 107, 108 in the form of scissors having the pivot 132. Then, the stationary pivot pins 121, 122 at the end portion 118 of the second link 108 are forced or press-fitted into the engaging holes 129 formed in the front bearing portions 127 of the holder plate 125. This press-fitting of the pins 121, 122 into the holes 128 is effected utilizing elasticity of the resin materials of the end portion 118 (118A) and pins 121, 122 and the front bearing portions 127. Accordingly, it is difficult and cumbersome to achieve precise positioning of the pins 121, 122 with respect to the holes 129.
Similar difficulty is encountered when the sliding pins 115, 116 at the end portion 111 of the first link 107 are forced into the engaging grooves 128 formed in the rear bearing portions 126 of the holder plate 125, while utilizing the elastic property of the resin material.
After the linkage 106 is attached to the front and rear bearing portions 126 and 127 of the holder plate 125, the keytop 101 is attached to the linkage 106. Described more specifically, the stationary pivot pins 113, 114 of the first link 107 are forced or press-fitted into the engaging holes 104 at the front bearing portions 102 of the keytop 101, while the sliding pins 123, 124 of the second link 108 are forced or press-fitted into the engaging grooves 105 at the rear bearing portions 103 of the keytop 101. These press-fitting operations are also effected by utilizing the elastic property of the resin materials of the pins 113, 114, 123, 124 and the front and rear bearing portions 102, 103. Thus, similar difficulty is encountered when the pins 113, 114, 123, 124 are forced into the holes 104 and grooves 105.
As described above, the connection of the linkage 106 to the holder plate 125 and the connection of the keytop 101 to the linkage 106 are effected by utilizing the elasticity of the resin materials of the links 107, 108, holder plate 125 and keytop 101. Accordingly, the assembling procedure of the key switch of FIGS. 14-16 is difficult and time-consuming, leading to an increased cost of manufacture of the key switch and an increased cost of manufacture of a keyboard using the key switch.